Rodent repellent polyethylene



United States Patent 3,132,992 RODENT REPELLENT POLYETHYLENE Ellsworth E. Kimznel, Pittsburgh, Pa, assignor to Koppers Company, Inc., a corporation of Delaware N0 Drawing. Filed May 19, 1960, Ser. No. 30,061 1 Claim. (Cl. 167-46) This invention relates to polyethylene, andmore partioularly, to polyethylene having increased resistance to penetration by rodents and other depredative animals.

Polyethylene has, for a long time, been used as a material for packaging and containing goods because such material is light in weight, has excellent clarity and strength, and provides ease in handling. The use of polyethylene has been restricted, however, because polyethylene normally does not resist attack by rodent. Polyethylene has been used heretofore, for example, as a container for silage on farms. Silage is made by storing of a green chopped and unchopped forage for a period of about four to seven months whereby fermenation will occur. Exposure of silage to air will result in spoilage of the forage. The use of towers or silos has been the common method of occluding air from the forage. The use of horizontal trenches, bunkers and stacks for production of silage has increased rapidly during the past few years. Horizontal silos, however, have a large area of exposed surface as compared to tower silos. The increase in surface area requires an eifective barrier to prevent excessive losses of the silage. Polyethylene film is advantageous for such a barrier. However, polyethylene is susceptible to penetration by rodents and other depredative animals and spoilage of the silage results if a penetration of the polyethylene is made.

The stonage of animal and poultry feeds in polyethylene containers has not been feasible heretofore because of the high incidence of mice and rats in farm areas. Although cotton and burlap have been used for farm storage and do offer some resistance to rodent penetration, the lack of a good solution to the problem of rodent penetration, has necessitated maintaining a minimum inventory of feed by the farmer to minimize damage by rodents.

Attempts to make a plastic film rodent repellent heretofore, have not met with commercial success because the high concentration of additives used have resulted in excessively high costs.

It has now been discovered that polyethylene containing 2% by weight of a compound selected from the group consisting of trinitrobenzene aniline complex and tributyl tin chloride, is an effective rodent repellent. Surprisingly, articles made from polyethylene containing, for example, trinitrobenzene aniline complex is concentration as low as 2%, show a reduction in penetration by mice and other foraging animals, as great as 85%, when compared with similar articles of untreated polyethylene.

The amount of compound selected from the group consisting of trinitrobenzene aniline complex and tributyl tin chloride additive contained in the polyethylene, can be as low as 1% by weight of the film but advantageously is 2%. If less than 1% of the additive is contained in the polyethylene, the eifeotiveness of the products to resist penetration by rodents, is lowered; and if more than 2% of the additive is contained in the polyethylene, the amount of protection which the products afford molding operations.

3,132,992 Patented May 12,1964

against rodents, does not materially increase. In addition, if large amounts of the additive are used, the eco nomical advantage of the use of the treated film as a rodent-repellent material, is nullified by the cost of the raw materials. The ability of a polyethylene containing between 1% and 2% by Weight of the additive to effectively repel penetration by rodents, is remarkable, in view of the fact that rats and mice have the ability to penetrate barriers containing any one of a Whole group of com pounds that should be highly noxious and/or highly toxic to the rats and mice. Rats and mice have been known to discard immediately material removed from a barrier during the penetration thereof without ingesting any of it and apparently Without tasting any of the obnoxious material that the barrier may contain.

The additives of this invention are available in commercial quantities. fIrinitrobenzene aniline complex is a solid orange-red crystal material having a melting point between 122 C. and 126 C. Tributyl tin chloride is a Water insoluble liquid which is thermally stable at 300 C.

Any of the commercially available polyethylenes may be used in the practice of this invention. The particular properties of the polyethylene to be used will depend upon the equipment to be used in producing articlesfrom the polyethylene and also the specifications demanded by the ultimate consumer.

The novel rodent-repellent polyethylene of this inven-' tion may be made by blending the additivewith polyethylene in any of the conventional manners of blending solid materials with polyethylene, for example, pellets of polyethylene may be placed in a mixer, such as a Banbury mixer, along with the additives and mixed, and then the mixture extruded in a conventional manner. The blend of additive and polyethylene may be extruded directly as sheets or film, or may be extruded as a rod which is chopped into pellets for use by fabricators of polyethylene articles. Alternatively, polyethylene pellets may be placed in a Bolling two-roll mill and compounded into sheet form, whereupon additive is added to the compounded sheet until the desired concentration is reached. The additive containing polyethylene sheet may then be removed from the rolls and used as a rodent-repellent sheet material. The polyethylene of this invention may be made into ntunerous useful articles by conventional processes of injection molding or extrusion. A film of polyethylene containing 2% by weight of the additive may be made into a package, for example, by heat-sealing the edges of the polyethylene.

A rodent-repellent material can be made by laminating by conventional extrusion laminating methods, the polyethylene film of this invention to cotton, burlap, paper, or the like. The thus-laminated stnucture can be made into individual packages for storage, or a protective tarpaulin can be made to cover or surround other packages, which are subject to rodent attack during storage in Warehouses, depots, or outdoor storage areas.

The formation of articles from thenovel polyethylene of this invention, is not limited to extrusion operations, but will include conventional blow-molding and injecting For example, the additive containing polyethylene may be injection molded into individual rigid protective containers, such as garbage cans, that are susceptible to rodent penetnation.

The following examples further illustrate this invention:

EXAMPLE 1 Ten pounds of low-density extrusion grade polyethylene by rodents. These tests are significant because the laboratory tests represent optimum conditions for rodent attacks. The reduction in rodent damage obtained in laboratory tests, has :been found to be greatly improved Sold y QI P Company, l the trade 5 when tested materials are placed under field tests. 05 Dylan, and P of tflllltfobenzene 33111116 The excellent rodent repellent properties of the poly- PP F, were thoroughly l 111 a P 'Y mlXerethylene of this invention are further complemented by E mtm'e was then extrudd a 9 1110b f the fact that the tensile strength properties of the polya 1211 barrel length to bifTel dlamster mm) 5 ethylene having the additives incorporated therein have a dle manager of two Inches, 920 p Opemng 10 in no way been changed or ideleterio usly afiected when at a temperature of 4 Produce a compared with a like polyethylene containing no rodent hE-Vmg Thlckfifi$ 3 T1115 film P repellent additives. Table III below shows comparative th1'011ghQut 2% y Welght 0f tnmtfobenzene amhne data obtained from tests conducted upon additive-treated plex. Similarly, 10 pounds of the polyethylene treated and t ted polyethylene film: with .02 pound of tributyl tin chloride were also prepared A control 10 pounds of the polyethylene with- 10 Table HI TENSILE STRENGTHS 0F POLYETHYLENE FILM out an additive were prepared in a like manner.

The repellent-treated and untreated film were made Tensile Tensile into small envelopes and filled with a quantity of oats Sample sttrg ng tih s t l and ground fox chow suficient to sustain a conditioned a a test animal 24 hours. The envelopes were then sealed and tested by exposing a single-treated and untreated Polyethylene (no additives) 1,070 1,270 bag to an individually caged house mouse for a 24 hour Polyethylene +2%tr1mtr0benzene amhne co v plex 1,110 1,260 period. The results f a er f tests using Polyethylene +2% tributyltin chloride 1,100 1,280 these test animals, are shown in the -followmg table:

Table I Number of Bags Penetrated Total Damage Number Number Reduc- Iolyethyleno Rodent of Bags tion,

Animals Treated Un- Both Pene- Percent treated trated 2% Trlnitrobenzene Aniline House Mice. 51 3 47 1 52 85 Complex vs. Untreated Polyethylene.

, Do do 51 1 43 7 58 72 2% Trlbutyl Tin Chloride vs. do 52 4 8 60 60 Untreated Polyethylene.

Do do 52 0 43 9 61 70 The procedure as hereina'bove-described was followed The 2% concentration of additive in polyethylene, will except that Norway rats were used as the test animals. impart to the polyethylene a pale color, which color is The amount of food, however, was insufficient to sustain derived from the additive. For example, when a blend a test rat for a 24 hour period. These rats are known of polyethylene and trinitrobenzene aniline is extruded to be among the most aggressive and voracious of all as a film, the film will have a reddish or pink tint. The rodents. Therefore, any reduction in damage to macolor of the polyethylene will provide a distinctive charterials susceptible to rodent attack, is a very material :aoteristic to the polyethylene, whereby it will be easily improvement, and particularly so, when this damage is recognizable as a rodent repellent material. shown to be reduced by tests made under ideal condi For outdoor applications, the preferred compositions tions, where attack of the test specimens by the Norway include the use of carbon black dispersed in the polyrat would normally :be inevitable. The results of this ethylene to prevent the loss of strength through ultraseries of tests are described in Table II: violet light exposure.

Table 11' Number of Bags Penetrated Total Damage Number Number Reduc- Polyethylene Rodent of Bags tion,

Animals Treated Un- Both Pene- Percent treated trated 2% Trlnitrobanzene Aniline Norway Eats. 42 9 21 12 54 22 Complex vs. Untreated Polyethylene.

2% Tributyl Tin Chloride vs. -do- 20 2 11 7 27 33 Untreated Polyethylene.

In the above tables, the damage reduction R, was The foregoing has presented a novel economical rodent calculated by the formula: repellent polyethylene which can be employed successfully V T as a protective cover in rural and agricultural areas where R: stored materials are vulnerable to rodent attack. The

N where V represents the number of times untreated bags Polyethylene be used as Separate Packaging only were penetrated in a cage, T represents the number 7 mammal or as Protective tarp under and around other of times treated bags only were penetrated in a cage, and N equals the total number of bags penetrated.

As shown in the :above table, polyethylene films containing 2% trinitrobenzene aniline complex or 2% tin chloride, are highly elfective in preventing penetration packaged materials. An especially strong, durable, and repellent package or tarpaulin, can be made from a film laminated cotton or burlap material. This film can be applied to the inner or outer Walls of storage buildings to act as a protective coating against entry of rodents.

into the buildings. Small cracks, openings, and window areas in buildings can be quickly sealed to provide a permanent or temporary deterrent to entry by marauding rodents.

What is claimed is:

Polyethylene which is capable of protecting goods from attack and destruction by rodents, which comprises: polyethylene containing substantially uniformly distributed throughout from 1% to 2% by weight of tributyl tin chloride.

Canada May 15, 1956 OTHER REFERENCES Welch: Journal of Agn'cvultunal vol. 2, 1954, pages 142-149.

and Food Chemistry, 

